The present invention relates to a silicone-based working fluid composition or, more particularly, to a working fluid composition comprising organopolysiloxanes and capable of being used in a hermetically sealed condition at high temperatures which can be used also as a base oil for the preparation of a silicone grease.
It may be too much to say that silicone fluids are much superior in respect of the heat resistance to conventional mineral oils as well as oils originating in animals and plants. Even these silicone fluids are not safe from oxidation when exposed to a high temperature atmosphere at 200.degree. C. or higher resulting in gradual degradation of the quality so that it is eagerly desired to develop a silicone fluid composition usable as a lubricating oil or a working fluid at high temperatures with sufficient durability or serviceable life.
Of course, various proposals and attempts have been made to provide a means for significantly improving the heat resistance of silicone fluids. For example, U.S. Pat. No. 3,328,350 discloses a method in which a silicone fluid is admixed with an organopolysiloxane having specific aromatic-substituted amino groups as the pendant groups on the polysiloxane to be imparted with improved heat resistance. The silicone fluid composition described there can indeed exhibit excellent heat resistance under a condition of good contacting with atmospheric air but the effect of preventing viscosity decrease at high temperatures is rather poor when the fluid composition is under a hermetically sealed or semi-sealed condition without free contacting with air.